OBJECTIVE: To examine the effects of leptin on LHRH release in vivo. RESULTS Because of increasing interest in leptin, we examined the effects of leptin on LHRH release in the ovariectomized adult rhesus monkeys in vivo. Leptin at 10 pM, 1 nM, and 100 nM was infused for 20 min into the S-ME through a push cannula, while perfusates were collected through a pull cannula. Leptin stimulated LHRH release in a dose-responsive manner. Leptin at 10 pM increased LHRH release (50%) peaking at 20 min after the initiation of the infusion, and leptin at 1 nM and 100 nM increased LHRH release (100% and 180%, respectively), both peaking after the first 10 min of the infusion. Data from this study indicate that leptin may play an important role in linking a metabolic signal with reproductive function. FUTURE DIRECTIONS We plan to examine the causal relationship between leptin effects and NPY release. KEY WORDS leptin, pulsatile LHRH release, monkey hypothalamus.